Most of those limits are for noise levels and surface conditions.
> According to official statistics from 2018, unlimited highways in Germany claimed about 71% of fatalities on highways.[86] However, autobahns without speed limits also account for 70% of the entire autobahn network, which puts the high proportion of collision fatalities on stretches without speed limits into perspective.[86] However, the often resulting thinking that speed limits would not make roads significantly safer is a fallacy, since it is precisely those roads that have a high volume of traffic and thus a high risk of collisions that are given speed limits.
And for surface conditions, repave the road.